1. Field of the Invention
The present invention relates to a balancing device for a four-cycle engine and, more particularly, relates to a balancing device for canceling out a vibromotive force generated from a four-cycle V-type eight-cylinder engine having a bank gap of 90 degrees.
2. Description of the Related Art
When a plane crank configuration is adopted in a four-cycle V-type eight-cylinder engine having a bank gap of 90 degrees in which axial centers of all crank pins are disposed on the same plane, the operation cycle of the two banks occurs at every 180 degrees of crankshaft rotation, and intake and exhaust operations take place alternately. According to this construction, because the intake and exhaust operations happen at equal intervals, no exhaust interference is caused, and thus, the engine so constructed is advantageous in obtaining a high output.
On the other hand, in the V-type eight-cylinder engine using the plane crank configuration, in a case where a plane is disposed perpendicularly which passes through the center of a crankshaft so as to bisect the bank gap angle of the engine, unbalanced forces produced by a horizontal component of an inertia force generated by reciprocating pistons in the two banks of the engine cannot be cancelled out only by counterweights provided on the crankshaft. This unbalance, however, is identical to unbalanced forces produced by a secondary inertia force generated in a condition in which the cylinders of an in-line four-cylinder engine are made horizontal, and therefore, it can be cancelled out by rotating two balance shafts disposed on a perpendicular plane in opposite directions to each other by adopting the theory of the secondary balancer for a conventional in-line four-cylinder engine (refer to Japanese Patent Unexamined Publication No. Hei. 8-193643).
With the aforesaid conventional balancing device, however, in which consideration is given only to the balancing of the inertia force from the piston system, unbalanced vibrations cannot be eliminated which are caused by the inertia force from the valve system. In particular, in the case of a V-type engine in which a closed valve resting mechanism is provided for a valve system on one of the banks thereof, the inertia forces of the valve systems on the two banks become different, and this makes it more difficult to eliminate unbalanced vibrations caused by the inertia forces from the valve systems.
As is disclosed in Japanese Utility Model Unexamined Publication No. Sho.64-36630, a balancing device is also known in which equivalent inertia masses are provided for the valve systems. This balancing device is, however, provided separately from a balancing device for the piston systems, and therefore, it is inevitable that the construction of the engine becomes complicated.
The present invention has been made with a view to solving the problem inherent in the prior art, and an object thereof is to provide a balancing device for a four-cycle engine which can control vibrations of the engine at a further improved level without involving any complexity in construction of the engine.
With a view to attaining the above object, according to a first aspect of the present invention, there is provided a balancing device for a four-cycle V-type eight-cylinder engine having a bank gap angle of 90 degrees, in which there is provided, on a common rotating shaft, a part (an equivalent inertia mass P as described in a mode for carrying out the invention) for generating a first inertia force for offsetting a residual secondary inertia force from piston systems and a part (equivalent inertia masses VH, VV as described in the mode for carrying out the invention) for generating a second inertia force for canceling out a residual inertia force from valve systems. According to this construction, since balancing devices for the piston and valve systems can be integrated into one device, no complicated construction can be involved.
In particular, in a case where an engine has asymmetrically constructed valve systems on the two banks thereof, with a construction in which weights (eccentric weights 91, 92 as described in the mode for carrying out the invention) each having a center of gravity positioned in a direction of a vector sum of first and second inertia forces are provided on the rotating shaft, the configuration of the rotating shaft does not have to be complicated. In addition, with a construction in which the rotating shaft has parts (third weights 401, 402 as described in the mode for carrying out the invention) provided on a most extreme end thereof for generating a third inertia force for offsetting a residual secondary inertia couple from the valve systems, it is possible to attain the control of vibrations of the engine at a further improved level.
In addition to this, the above-mentioned object can be achieved by a balancing device for a four-cycle engine according to a second aspect of the present invention comprising:
a common rotating member rotatable in accordance with the rotation of a crankshaft of the engine, the common rotating member including:
a first portion for generating a first inertia force which offsets a residual secondary inertia force caused by piston systems when the engine is driven, and
a second portion for generating a second inertia force which offsets a residual secondary inertia force from valve systems when the engine is driven.
In the above-mentioned construction, it is preferable that the rotating member further comprises:
a third portion, which is disposed at its end portion, for generating a third inertia force which offsets a residual secondary inertia couple being caused by valve systems.
In the above-mentioned construction, it is preferable that the four-cycle engine is a four-cycle V-type engine, the valve systems are constituted by first and second valve systems which are asymmetrically constructed each other, the first valve system is disposed in one of the banks, and the second valve system is disposed in the other of the banks.
In the above-mentioned construction, it is also preferable that the rotating member is provided with at least one weight having a gravity of center positioned in a direction of a vector sum of vectors of the first inertia force and the second inertia force.
Further, in the above-mentioned construction, it is also preferable that the rotating member is provided with a third portion, which is disposed at its end portion, for generating a third inertia force which offsets a residual secondary inertia couple being caused by the first and second valve systems.
Further, in the above-mentioned construction, it is preferable that the first valve system disposed in one of the banks comprises a valve resting mechanism for maintaining intake and exhaust valves of the valve systems in a valve closed state. It is also preferable that the first valve system disposed on the one of the banks comprises a valve resting mechanism for creating a vacuum state within a combustion chamber by resting the operation of the valves when the piston is at a top dead center.
In the above-mentioned balancing device for a four-cycle engine, it is preferable that the rotating member is supported on crank bearing walls of the engine.
In the above-mentioned balancing device, the four-cycle engine is a four-cycle V-type eight-cylinder engine having a bank gap angle of 90 degrees, wherein the common rotating member comprises:
a first common rotating shaft rotated in a first direction in accordance with the rotation of the crank shaft and provided with a first weight member for generating a part of the first inertia force and a part of the second inertia force; and
a second common rotating shaft rotated in a second direction opposite to the first common rotating shaft with a second weight member for generating the remaining part of the first inertia force and the remaining part of the second inertia force.
In the balancing device, the valve systems may be constituted by first and second valve systems which are asymmetrically constructed in relation to each other, in which the first valve system is disposed in one of the banks and the second valve system is disposed in the other of the banks.
In the balancing device, each of the first and second weight members may have a center of gravity positioned in a direction of a vector sum of vectors of the first inertia force and the second inertia force.
In the balancing device, the first rotating shaft is provided with a third weight member at its end portion for generating a part of a third inertia force which offsets a residual secondary inertia couple being caused by the valve systems, and the second rotating shaft is provided with a fourth weight member at its end portion for generating the remaining part of the third inertia force.
Further, in the balancing device the first rotating shaft may be provided with a third weight member at its end portion for generating a part of a third inertia force which offsets a residual secondary inertia couple being caused by the valve systems, and the second rotating shaft is provided with a fourth weight member at its end portion for generating the remaining part of the third inertia force.
In the balancing device, the first valve system may comprise:
a valve resting mechanism for maintaining intake and exhaust valves of the valve systems in a valve closed state.
Further, in the balancing device, the first valve system preferably comprises a valve resting mechanism for creating a vacuum state within a combustion chamber by resting the operation of the valves when the piston is at top dead center.
Furthermore, in the balancing device the first and second rotating shafts are supported on crank bearing walls.